1. Field of the Invention
The present invention relates to a bit, and more particularly to a bit for removing damaged screws.
2. Description of the Prior Arts
Screws may be damaged due to many reasons, for example, the rotating force applied on the screws by the user is not smooth, the contacting angle between the screwdriver and the screw is incorrect, the tip head of the screwdriver is broken, and etc. All these factors can cause the damage of the screw, and the damaged screws cannot be screwed again, and the working efficiency for screwing the screws is inevitably decreased. U.S. Pat. No. 6,595,730 discloses a bit for removing damaged screws, as shown in FIGS. 1 and 2, the bit 10 has an hexagonal end which is to be held in a chuck of an electric tool, and another tip end of the bit 10 is formed with two recesses 11. The recesses each are defined by a planar scraping surface 12, 13 having a scraping edge 121, 131. An upward rounded surface 14 is defined between the scraping edges 121, 131. As shown in FIG. 3, the scraping edges 121, 131 of the bit 10 engage the slot or cross recess 21 of the damaged screw 20 and have a purchase and leverage on the head of the damaged screw 20 to break it away from its firm engagement with the object (not shown) and put it into rotation with the bit and back it out. However, in real operation, there is a need for improving this conventional bit, and the reasons are explained as follows:
First, the upward rounded surface 14 defined between the scraping edges 121, 131 is round-shaped, in other words, is in the shape of sector. The more closer to the outer edge of the upward rounded surface 14, the larger the distance between the scraping edges 121, 131 will be. In this case, the depth the bit 10 engaged in the slot or recess 21 of the damaged screw 20 is limited by the upward rounded surface 14, thus weakening the engaging force of the scraping edge 121, 131 acted on the damaged screw 20, and as a result, the leverage on the damaged screw 20 is less effective.
Second, the slot 21 of the screw 20 may be completely damaged and turned into a downward rounded surface, in this case, the conventional bit 10 is stopped by the upward rounded surface 14 and is unable to remove the damaged screw 20. In other cases, only the superficial portion of the slot 21 is damaged and the deep of the slot 21 is still in the shape of a slot (for example, the slot is a cross slot), at this moment, the bit 10 is also unable to engage the damaged slot 21, and as a result the screw 20 cannot be removed.
Third, the upward rounded surface 14 defined between the scraping edges 121, 131 is round-shaped, to remove the screw 20, the slot 21 of the screw 20 is likely to be damaged by the bit 10, to a great extent. Therefore, this conventional bit 10 is unable to remove such a screw 20 with a straight slot 21.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.